Hitherto, as techniques for starting the engine when the above-mentioned hybrid vehicle is travelling driven by a driving force from the motor only (hereinafter, referred to as “electric travelling”), the following ones are known.
Patent document 1 has disclosed an engine starting method for a hybrid vehicle. According to the engine starting method, an engine starting command is issued when an engine revolution speed reaches the startable revolution speed, and thereafter, vibrations accompanied with torque fluctuation generated in starting the engine is suppressed by gradually reducing an engagement force of a clutch serving as an engagement device.
Patent document 2 has disclosed an engine starting control device for a hybrid vehicle provided with a hybrid driving system configured by interposing a first clutch between the engine and the motor as an engagement device and by interposing a second clutch between the motor and driving wheels. According to the engine starting control device, when the engine is started during electric travelling in which the hybrid vehicle is driven by the motor, a required driving force is achieved within a range of driving force which can be achieved by the electric travelling; moreover, by slide-fastening the first clutch to perform the engine starting, the driving force can be prevented from getting lost against the willing of a driver at the time of the engine starting.